Wearable sports monitors are used by many amateur and professional sportsmen and sportswomen for collecting data on and for analyzing sports performances to assist training. For example, automatic tracking of distance travelled has become common in outdoor sports due to satellite-positioning receivers. Swimming forms a particular challenge in this respect, because it is usually carried out indoors, where satellite positioning does not work. Swimming distance can, however, be determined using for example acceleration sensor, predefined information on the pool length and recognition of the swimmer's turns at the ends of the pool.
Another challenge in swimming monitoring is the characterization of swimming style, i.e., whether front crawl, breast stroke, butterfly stroke, back crawl or one of the other possible swimming styles, is used. This is a difficult task because not only the styles are quite similar as concern the strokes of the swimmer from the viewpoint of “blind” accelerometers, but because there is great personal stroke variation between swimmers. There are no robust and computationally light methods available that would reliably determine the swimming style based on measuring the properties of strokes.
US 2004/0020856 discloses a swimming monitor comprising an acceleration-based stroke sensing circuit and magnetic field-based lap sensing circuit. The lap sensing circuit is adapted to detect 180 degrees changes in magnetic bearings in order to detect the end points of the pool. The device does not allow for swimming style classification. U.S. Pat. No. 6,955,542 discloses a system for monitoring repetitive movement such as swimming strokes using a two-dimensional accelerometer sensor preferably mounts on the swimmer's back. The system may also identify strokes, movement patterns and start or stop times of movements and provide feedback for the user in real time.
U.S. Pat. No. 7,980,998 discloses a training support device comprising a sensing unit adapted to repeatedly measure movement of a body part of a swimmer using an accelerometer, compass and optimally a gyroscope. The device is configured to determine the exact location and orientation of the body part in order to help to improve movements. The device may also determine the periodicity of movements and statistical information on the performance.
US 2010/0210975 discloses a swimming performance monitoring system utilizing a three-dimensional accelerometer. The system comprises stroke recognizer that is able to analyze accelerometer data for detecting strokes and finding turns and swimming style. The stroke recognizer applies rules directly on filtered accelerometer data. However, the success of this approach, in particular in style classification, depends heavily on how well the personal stroke of the swimmer matches with the predefined rules.
The systems according to the known art are either not capable of determining swimming styles and/or turns of swimmers, or their capability to detect these or other swimming-related parameters depends heavily on the personal properties of the swimmer.
Thus, there is a need for improved devices and methods for assisting automating determination of swimming parameters.